Luis Barcenas is a former senator, and was the treasurer of the Popular Party from 1990 to 2009.
BBC: Q&A: Spain's opposition tells PM to go
2.
Mr Barcenas stepped down as treasurer in 2009 after being implicated in a separate corruption case known as the Gurtel scandal.
BBC: Spain: Rajoy man Barcenas arrives for questioning
3.
Money was allegedly paid by outside firms via two former treasurers including Luis Barcenas, who stepped down in 2009 and is currently under investigation for money-laundering.
BBC: Spain ruling party faces inquiry over 'slush fund'